U.S. patent number 6,962,583 [Application Number 10/731,455] was granted by the patent office on 2005-11-08 for cataract extraction apparatus and method with rapid pulse phaco power.
This patent grant is currently assigned to Advanced Medical Optics, Inc.. Invention is credited to Kenneth E. Kadziauskas, Paul Rockley, James W. Staggs, Mark E. Steen.
United States Patent |
6,962,583 |
Kadziauskas , et
al. |
November 8, 2005 |
Cataract extraction apparatus and method with rapid pulse phaco
power
Abstract
Apparatus and method for the removal of lens tissue includes a
first handpiece having a laser emitting probe sized for insertion
into a lens capsule and radiating a lens therein. The laser
emitting probe includes a lumen for introducing irrigation fluid
into the lens capsule. A second handpiece includes a pulsed
controlled vibrated needle for insertion into the lens capsule and
emulsifying laser eradiated lens tissue. The vibrated needle
includes a lumen therethrough for aspiration of emulsified lens
tissue and irrigation fluid.
Inventors: |
Kadziauskas; Kenneth E. (Coto
de Caza, CA), Steen; Mark E. (Chino Hills, CA), Rockley;
Paul (Corona del Mar, CA), Staggs; James W. (Laguna
Niguel, CA) |
Assignee: |
Advanced Medical Optics, Inc.
(Santa Ana, CA)
|
Family
ID: |
36181727 |
Appl.
No.: |
10/731,455 |
Filed: |
December 8, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
949405 |
Sep 7, 2001 |
6733491 |
|
|
|
Current U.S.
Class: |
606/6; 604/22;
606/4; 606/128; 606/107; 606/12 |
Current CPC
Class: |
A61F
9/008 (20130101); A61F 9/00745 (20130101); A61B
2017/320084 (20130101); A61B 2217/005 (20130101); A61B
2217/007 (20130101); A61B 2017/32007 (20170801); A61F
2009/0087 (20130101); A61F 2009/00887 (20130101) |
Current International
Class: |
A61F
9/008 (20060101); A61F 9/007 (20060101); A61M
1/00 (20060101); A61B 018/18 () |
Field of
Search: |
;606/4-6,10-12,107,108,127,128,167-171,178 ;607/88,89
;604/20-22,27,28,30 ;600/398-402 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Farah; A.
Attorney, Agent or Firm: Advanced Medical Optics, Inc.
Parent Case Text
The present application is a continuation-in-part of U.S. Ser. No.
09/949,405 filed Sep. 7, 2001 now U.S. Pat. No. 6,733,491.
Claims
What is claimed is:
1. Apparatus for the removal of lens tissue, said apparatus
comprising: a first handpiece including a laser emitting probe
sized for insertion into a lens capsule and radiating a lens
therein, said laser emitting probe including a lumen for
introducing an irrigation fluid into said lens capsule; and a
second handpiece including a vibrated needle for insertion into
said lens capsule and emulsifying lens tissue, said vibrated needle
including a lumen therethrough for aspiration of emulsified lens
tissue and irrigation fluid; a power source for providing pulsed
electrical power to the second handpiece; an input for enabling a
surgeon to select an amplitude of the electrical pulses; a control
console, interconnected with both the first handpiece and second
handpiece for controlling simultaneous and sequential operation of
the first handpiece and second handpiece and in response to the
selected pulse amplitude for controlling a pulse duty cycle of
power supplied to the second handpiece, an off duty cycle being
controlled to ensure heat dissipation before a subsequent pulse is
activated.
2. The apparatus according to claim 1 wherein said control console
provides a pulse repetition rate of between about 25 and 2000
pulses per second to said second handpiece.
3. The apparatus according to claim 1 wherein said input enables a
linear selection of pulse amplitude.
4. The apparatus according to claim 1 wherein said second handpiece
includes a transducer for driving said vibrated needle at
ultrasonic frequencies.
5. The apparatus according to claim 1 wherein said laser emitting
probe comprises fiber optics.
6. The apparatus according to claim 5 wherein the laser emitting
probe lumen is disposed through said fiber optics.
7. A method for removing lens tissue from a lens capsule, said
method comprising: inserting a laser emitting probe having an
irrigation lumen into said lens capsule; inserting a vibratable
needle having an aspiration lumen into said lens capsule;
introducing irrigation fluid into said lens capsule through said
irrigation lumen; softening said lens tissue by exposure to laser
energy from said laser emitting probe; vibrating the needle to
emulsify softened lens tissue; providing a power source for
providing pulsing electrical power for vibrating the needle;
providing an input for enabling a surgeon to select a pulse
amplitude of the pulsing electrical power; controlling operation of
the laser emitting probe and vibratable needle simultaneously and
sequentially in order to effect emulsification of the lens tissue;
controlling a pulse duty cycle of said power source in response to
the selected pulse amplitude, an off duty cycle being controlled to
insure heat dissipation before a subsequent pulse is activated; and
aspirating emulsified lens tissue and irrigation fluid from said
lens capsule through said aspiration lumen.
8. A method for removing lens tissue from a lens capsule, said
method comprising: inserting a laser emitting probe having an
irrigation lumen into said lens capsule; inserting a vibratable
needle having an aspiration lumen into said lens capsule;
introducing irrigation fluid into said lens capsule through said
irrigation lumen; fracturing said lens tissue by exposure to laser
energy from said laser emitting probe; providing a power source for
pulsing electrical power for vibrating the needle; providing an
input for enabling a surgeon to select a pulse amplitude of the
pulsing electrical power; vibrating the needle to emulsify
fractured lens tissue; controlling the fracturing of said lens
tissue and emulsification of fractured lens tissue simultaneously
and sequentially in order to effect emulsification of the lens
tissue; controlling a pulse duty cycle of said power source in
response to the selected pulse amplitude, an off duty cycle being
controlled to insure that dissipation before a subsequent pulse is
activated; and aspirating emulsified lens tissue and irrigation
fluid from said lens capsule through said aspiration lumen.
Description
The present invention generally relates to apparatus and method for
extracting cataract tissue and more particularly is directed to
combined use of vibrational and laser energy to effect cataract
removal.
An eye generally includes an anterior chamber and a posterior
chamber separated by a lens contained in a lens capsule. The lens
functions to focus incoming light onto a retina disposed on a rear
wall of the posterior chamber.
Cataracts cause the lens of an eye to become clouded, which
interferes with proper transmission and focusing of light on the
retina. A common practice to alleviate this condition is by
surgically removing the cataractic lens and replacing it with an
artificial intraocular lens.
Early lens removal was effected through manual extraction which
required a wound of about 12 mm in length. This large opening can
result in corneal or sclera tissue damage.
Externally applied laser radiation has been used to soften a
cataract lens before manual extraction therefor. See U.S. Pat. Nos.
4,825,865, 5,057,098, 5,112,339, 5,139,504 and 5,403,307. Such
manual extraction requires large entry wounds as hereinabove
noted.
Phacoemulsification, on the other hand, enables the removal of a
cataractic lens through a much smaller incision, for example
between about 2.5 to about 4 mm. In this procedure, a needle is
inserted through the incision into a lens capsule and the needle is
ultrasonically vibrated to mechanically emulsify the lens. Once
fragmented, or emulsified, the lens material is aspirated through a
lumen through the phacoemulsification needle.
While emulsifying the lens and aspirating lens fragments, a
simultaneous flow of irrigation fluid into the lens capsule is
provided around the needle through an annulus established by a
sleeve concentrically disposed over the needle. This flow of liquid
into the eye is necessary to prevent collapse of the anterior
chamber of the eye during aspiration. In addition, the irrigation
fluid cools the needle in order to prevent any thermal damage of
the corneal or scleral tissue. While the sleeve surrounding a
phacoemulsification needle provides the important function of
establishing an annulus for introducing irrigation fluid into the
lens capsule and also enlarges the overall diameter of the sleeve
needle for which an incision must be made.
In addition, when irrigation fluid is introduced proximate the
emulsifying needle tip, the immediate area in front of the needle
is roiled. This occurs because of the counter-current flow of fluid
being aspirated by the needle itself and the irrigation fluid being
introduced over the surface of the needle. Needle vibration causes
a cloud of debris which is roiled by the incoming infusion fluid
which lessons the physicians visual acuity of the end of the needle
which can slow the procedure.
The present invention provides for the combined use of laser and
vibrational energy to remove cataractic lens tissue and overcomes
the drawbacks of a sleeved phacoemulsification needle. In addition,
rapid pulsation of the vibratant needle is controlled to insure
heat dissipation sufficient to present tissue damage.
SUMMARY OF THE INVENTION
Apparatus in accordance with the present invention for the removal
of lens tissue generally includes a first handpiece including a
laser emitting probe sized for insertion into a lens capsule and
radiating lens tissue therein. In addition, the laser emitting
probe includes a lumen for introducing an irrigation fluid into the
lens capsule.
In combination therewith, a second handpiece is provided which
includes a vibrated needle for insertion into the lens capsule and
emulsifying lens tissue that has been softened, or fractured, by
the laser radiation. The vibrated needle includes a lumen
therethrough for aspiration of the emulsified lens tissue and
irrigation fluid.
A power source is provided to provide pulsed electrical power to
the second handpiece along with an input for enabling a surgeon to
select an amplitude of the electrical pulses.
A control console is provided and interconnected with both first
and second handpieces for controlling irrigation and aspiration
rates and enabling simultaneous sequential operation of the laser
emitting probe and the vibrated needle. In this manner,
particularly hard or lens portions, that are resistant to
emulsification, may be preconditioned for emulsification by laser
radiation. The softening of lens tissue by laser is well known as
set forth in the hereinabove referenced U.S. patents.
In addition, the control console is structured and functions in
response to the selected pulse amplitude for controlling a pulse
duty cycle of power supplied to the second handpiece, an off duty
cycle being controlled to ensure heat dissipation before a
subsequent pulse is activated.
Because irrigation fluid is not simultaneously introduced proximate
the vibrating needle, as is the, case in prior art devices, no
disturbance or churning of fluid occur which may provide for a
"milky cloud" at the end of the needle which can tend to lessen
visual acuity, which in turn, may interfere with the accuracy of
the phacoemulsification by a physician.
Preferably the second handpiece includes a transducer for driving
the vibrating needle at ultrasonic frequencies and the laser
emitting probe comprises fiber optics with a irrigation lumen
therethrough.
A method in accordance with the present invention for removing lens
tissue from a lens capsule generally includes the steps of
inserting a laser emitting probe having an irrigation lumen into
the lens capsule along with a vibratable needle having an
aspiration lumen.
Irrigation fluid is introduced into the lens capsule and the lens
is softened or fractured by exposure to laser energy from the laser
emitting probe.
The needle is vibrated to emulsify the lens tissue which is
thereafter aspirated along with the irrigation fluid through an
aspiration lumen in the vibratable needle. A pulse duty cycle
provided to the needle is controlled in response to a selected
pulse amplitude to provide an off duty cycle enabling heat
dissipation before a subsequent pulse is activated.
The lens tissue may be exposed to laser radiation and emulsified
simultaneously or the laser exposure may be intermittent and in a
sequential manner. That is, the tissue may first be repeatedly
exposed to laser radiation and thereafter emulsified.
BRIEF DESCRIPTION OF THE DRAWING
The advantages and features of the present invention will be better
understood by the following description when considered in
conjunction with the accompanying drawing in which:
FIG. 1 is a diagram of apparatus in accordance with the present
invention generally showing a first handpiece for inserting a laser
emitting probe into a lens capsule along with introducing an
irrigation fluid into the lens capsule along with a second
handpiece for inserting a vibratable needle into the lens capsule
for emulsification of lens tissue and aspiration of emulsified
tissue and irrigation fluid.
FIG. 2 is a functional block diagram of a control system for the
second handpiece in accordance with the present invention;
FIG. 3 is a functional block diagram of an alternative embodiment
of a phacoemulsification system in accordance with the present
invention which includes apparatus for providing irrigation fluid
at more than one pressure to a handpiece;
FIG. 4 is a flow chart illustrating the operation of the
occluded-unoccluded mode of the phacoemulsification system with
variable aspiration rates;
FIG. 5 is a flow chart illustrating the operation of the
occluded-unoccluded mode of the phacoemulsification system with
variable ultrasonic power levels;
FIG. 6 is a flow chart illustrating the operation of the variable
duty cycle pulse function of the phacoemulsification system;
FIG. 7 is a flow chart illustrating the operation of the
occluded-unoccluded mode of the phacoemulsification system with
variable irrigation rates;
FIG. 8 is a plot of the 90 degree phase shift between the sine wave
representation of the voltage applied to a piezoelectric
phacoemulsification handpiece and the resultant current into the
handpiece;
FIG. 9 is a plot of the phase relationship and the impedance of a
typical piezoelectric phacoemulsification handpiece;
FIG. 10 is a block diagram of improved phase detector circuitry
suitable for performing a method in accordance with the present
invention;
FIG. 11 is a plot of phase relationship as a function of frequency
for various handpiece/needle loading;
FIG. 12 is a function block diagram of a phase control
phacoemulsification system utilizing phase angles to control
handpiece/needle parameters with max phase mode operation;
FIG. 13 is a function block control diagram of a phase control
phacoemulsification system utilizing phase angles to control
handpiece/needle parameters with a load detect method; and
FIG. 14 is a function block control diagram of a pulse control
phacoemulsification system.
DETAILED DESCRIPTION
With reference to FIG. 1 there is shown apparatus 10 for the
removal of lens tissue 12. The apparatus 10 generally includes a
first handpiece 14 which includes a laser emitting probe 18 for
insertion into a lens capsule 22 for radiating the lens tissue 12.
The handpiece 14 may include any suitable laser, such as, a Er:YAG
laser for providing laser energy to the probe 18 which includes
fiber optics for transmitting the laser energy into the lens
capsule 22 and lens 12.
A lumen 26 through the probe 18 is provided for introducing an
irrigation fluid, indicated by the arrow 30, into the lens capsule
22. Power and irrigation fluid are provided to the handpiece 14
through lines 32, 34 connected to a control console 36. The control
counsel 36 may be of any suitable type, such as for example, one
manufactured by Allergan, Inc. under the trade name
Sovereign.RTM..
A second handpiece 40 includes a vibrated needle 42 for emulsifying
lens tissue 12. Any suitable handpiece may be utilized, such as for
example, one sold by Allergan, Inc. under the trade name
Sovereign.RTM.. The handpiece 40 is interconnected to the console
36 and controlled thereby through a power line 42. A lumen 44
through the needle 42 is provided for aspiration of emulsified lens
tissue 12 and irrigation fluid as indicated by the arrow 46. Vacuum
is provided by the console through an aspiration line 50
interconnecting the handpiece 40, needle lumen 44 to the console
36.
In operation, the laser emitting probe is utilized to soften, or
fracture selected portion of the lens which are thereafter
emulsified by the needle 42 and aspirated through the lumen 44 and
line 50. The laser probe 18 and emulsifying needle 42 may be
operated simultaneously to effect lens removal or in a sequential
manner in which the lens 12 is preferably radiated by laser light
and thereafter emulsified by the vibrating needle 42.
It should also be noted that since the needle 42 does not include a
conventional sleeve (riot shown) a smaller incision or wound 54 is
enabled. The wound size may be a small as. 1.25 mm which is to be
compared with conventional sleeve needle (not shown) which require
a slit or wound opening (not shown) of about 21/2 to 3 mm.
A combined use of the laser emitting probe 18 emulsifying needle 42
increases the efficiency of lens removal, and is particularly
useful in cases in which the lens is of sufficient hardness such
that laser energy alone would not efficiently extract the
cataract.
The laser, in combination with ultrasonic energy, would result in a
lower total energy required to extract the cataract. This may also
reduce the likelihood of adverse events such as would burns. In
addition, smaller incisions may be used for cataract
extraction.
Turning now to FIGS. 2-4, and particularly to FIG. 2 thereof, there
is shown, in functional block diagram form, the control system or
console 36. The system has a control unit 112, indicated by the
dashed lines in FIG. 1 which includes a variable speed peristaltic
pump 114, which provides a vacuum source, a source of pulsed
ultrasonic power 116, and a microprocessor computer 118 that
provides control outputs to pump speed controller 120 and
ultrasonic power level controller 122. A vacuum sensor 124 provides
an input to computer 118 representing the vacuum level on the
output side of peristaltic pump 114. Suitable venting is provided
by vent 126.
As hereinafter described in greater detail, a phase detector 128
provides an input to computer 118 representing a phase shift
between a sine wave representation of the voltage applied to the
record 40 and the resultant current into the handpiece 40. The
block representation of the handpiece 40 includes the needle 42 and
a piezoelectric crystal (not shown), for ultrasonically vibrating
the needle.
The control unit 112 supplied ultrasonic power on line 132 to the
phacoemulsification handpiece 40 and needle 42. An irrigation fluid
source 134 is fluidly coupled to handpiece 40 and needle 42 through
line 136. The irrigation fluid and ultrasonic power are applied by
handpiece 40 to a patient's eye which is indicated diagrammatically
by block 138. Aspiration of the eye 138 is achieved by means of the
control unit peristaltic pump 114 through lines 140 and 142.
A switch 143 disposed on the handpiece 40 may be utilized as a
means for enabling a surgeon to select an amplitude of electrical
pulses to the handpiece via the computer 118, power level
controller 122 and ultrasonic power source 116 as hereinafter
discussed. It should be appreciated that any suitable input means,
such as, for example, a foot pedal (not shown) may be utilized in
lieu of the switch 143.
The computer 118 responds to preset vacuum levels in output line
142 from peristaltic pump 114 by means of signals from the
previously mentioned vacuum sensor 124. Operation of the control
unit in response to the occluded-unoccluded condition of handpiece
40 is shown in the flow diagram of FIG. 4.
As shown in FIG. 4, if the handpiece aspiration line 140 is
occluded, the vacuum level sensed by vacuum sensor 124 will
increase. The computer 118 has operator-settable limits for
aspiration rates, vacuum levels and ultrasonic power levels. As
illustrated in FIG. 4, when the vacuum level sensed by vacuum
sensor 124 reaches a predetermined revel as a result of occlusion
of the handpiece aspiration line 140, computer 118 instructs pump
speed controller 120 to change the speed of the peristaltic pump
114 which, in turn, changes the aspiration rate.
It will be appreciated that, depending upon the characteristics of
the material occluding handpiece 40, the speed of the peristaltic
pump 114 can either be increased or decreased. When the occluding
material is broken up, the vacuum sensor 124 registers a drop in
vacuum level, causing computer 118 to change the speed of
peristaltic pump 114 to an unoccluded operating speed.
In addition to changing the phacoemulsification parameter of
aspiration rate by varying the speed of the peristaltic pump 114,
the power level of the ultrasonic power source 16 can be varied as
a function of the occluded or unoccluded condition of handpiece 40.
FIG. 5 illustrates in flow diagram form the control of the
ultrasonic power source power level by means of computer 18 and
power level controller 122. It will be appreciated that the flow
diagram of FIG. 5 corresponds to the flow diagram of FIG. 4 but
varies the phacoemulsification parameter of the ultrasonic power
level.
With reference to FIG. 6, there is shown a flow diagram depicting
the control of the ultrasonic power source 116 to produce varying
pulse duty cycles as a function of selected power levels. As shown
in FIG. 6, and by way of illustration only, a 33% pulse duty cycle
is run until the power level exceeds a preset threshold; in this
case, 33%. At that point, the pulse duty cycle is increased to 50%
until the ultrasonic power level exceeds a 50% threshold, at which
point the pulse duty cycle is increased to 66%. When the ultrasonic
power level exceeds 66% threshold, the power source is run
continuously, i.e., a 100% duty cycle. Although the percentages of
33%, 50% and 66% have been illustrated in FIG. 6, it should be
understood that other percentage levels can be selected to define
different duty cycle shift points.
With reference to FIG. 14, when the computer 118 has been enabled
for pulse mode operation by an amplitude input via the switch 143,
the use of thermal tissue damage is reduced. In accordance with the
present invention, very rapid pulse duration is provided with
adequate energy to cut the tissue with kinetic or mechanical energy
but then the pulse is turned off long enough to eliminate the
thermal BTU's before the next pulse is activated. A surgeon may
vary the pulse amplitude in a linear manner via the switch 143 and
the control unit in response to the selected pulse amplitude,
irrigation and aspiration fluid flow rates, controlling a pulse
duty cycle. As hereinabove noted, an off duty duration or cycle is
provided to ensure heat dissipation before a subsequent pulse is
activated. In this way, increase amplitude will increase tip
acceleration and thus BTU's for tissue damaging heat generation.
That is, the surgeon can use linear power control to select the
correct acceleration necessary to cut through the tissue density
while the control unit provides a corresponding variation in pulse
width and "Off time" to prevent tissue de-compensation from heat.
The control unit is programmed depending on the phaco handpiece
chosen (total wattage) or the phaco tip (dimensions, weight). This
use of rapid pulsing is similar to how lasers operate with very
short duration pulses. Pulses may have a repetition rate of between
about 25 and 2000 pulses per second.
Turning back to FIG. 3, there is shown an alternative embodiment
150 of a phacoemulsification system, in accordance with the present
invention, and which incorporates all of the elements of the system
110 shown in FIG. 2, with identical reference characters
identifying components, as shown in FIG. 2.
In addition to the irrigation fluid source 134, a second irrigation
fluid source 135 is provided with the sources 134, 135 being
connected to the line 136 entering the handpiece/needle 130 through
lines 134a, 135a, respectively, and to a valve 138. The valve 138
functions to alternatively connect line 134a and source 134 and
line 135a and source 135 with the handpiece/needle 130 in response
to a signal from the power level controller 122 through a line
152.
As shown, irrigation fluid sources 134, 135 are disposed at
different heights above the handpiece 40 providing a means for
introducing irrigation fluid to the handpiece 40 at a plurality of
pressures, the head of the fluid in the container 135 being greater
than the head of fluid in the container 134. A harness 142,
including lines 144, 146 of different lengths when connected to the
support 148, provides a means for disposing the containers 134, 135
at different heights over the handpiece 40.
The use of containers for irrigation fluids at the various heights
is representative of the means for providing irrigation fluids at
different pressures, and alternatively, separate pumps may be
provided with, for example, separate circulation loops (not shown)
which also can provide irrigation fluid at discrete pressures to
the handpiece 40 upon a command from the power controller 122.
With reference to FIG. 6, if the handpiece 40 aspiration line 138
is occluded, the vacuum level sensed by the vacuum sensor 124 will
increase. The computer 118 has operator-settable limits for
controlling which of the irrigation fluid supplies 132, 133 will be
connected to the handpiece 40. It should be appreciated that while
two irrigation fluid sources, or containers 132, 133 are shown, any
number of containers may be utilized.
As shown in FIG. 7, when the vacuum level by the vacuum sensor 124
reaches a predetermined level, as a result of occlusion of the
aspiration handpiece line 138, the computer controls the valve 138
causing the valve to control fluid communication between each of
the containers 134, 135 and the handpiece/needle 130.
It should be appreciated that, depending upon the characteristics
of the material occluding the handpiece 40, as hereinabove
described and the needs and techniques of the physician, the
pressure of irrigation fluid provided the handpiece may be
increased or decreased. As occluded material 124, the vacuum sensor
124 registers a drop in the vacuum level causing the valve 138 to
switch to a container 134, 135, providing pressure at an unoccluded
level.
As noted hereinabove, it should be appreciated that more than one
container may be utilized in the present invention, as an
additional example, three containers (not shown) with the valve
interconnecting to select irrigation fluid from any of the three
containers, as hereinabove described in connection with the FIG. 2A
container system.
In addition to changing phacoemulsification handpiece 40 parameter
as a function of vacuum, the occluded or unoccluded state of the
handpiece can be determined based on a change in load sensed by a
handpiece/needle by way of a change in phase shift or shape of the
phase curve.
The typical range of frequencies used for phacoemulsification
handpiece 40 is between about 30 kHz and about 50 kHz. When the
frequency applied to the handpiece is significantly higher, or
lower than resonancy, it responds electrically as a capacitor. The
representation of this dynamic state is shown in FIG. 8 in which
curve 160 (solid line) represents a sine wave corresponding to
handpiece 40 current and curve 162 (broken line) represents a sine
wave corresponding to handpiece 40 voltage.
The impedance of the typical phacoemulsification handpiece 40
varies with frequency, i.e., it is reactive. The dependence of
typical handpiece 40 phase and impedance as a function of frequency
is shown in FIG. 9 in which curve 164 represents the phase
difference between current and voltage of the handpieces function
frequency and curve 166 shows the change in impedance of the
handpiece as a function of frequency. The impedance exhibits a low
at "Fr" and a high "Fa" for a typical range of frequencies.
Automatic tuning of the handpiece, as hereinabove briefly noted, is
typically accomplished by monitoring the handpiece electrical
signals and adjusting the frequency to maintain a consistency with
selected parameters.
In order to compensate for a load occurring at the tip of the
phacoemulsification handpiece, the drive voltage to the handpiece
can be increased while the load is detected and then decreased when
the load is removed. This phase detector is typically part of the
controller in this type of system.
In such conventional phase detectors, the typical output is a
voltage as proportional to the difference in alignment of the
voltage and the current waveform, for example, -90 degrees as shown
in FIG. 8. As shown in FIG. 9, it is important to consider that
during the use of the handpiece, the waveform is varying in phase
and correspondingly the output waveform is also varying.
Heretofore, the standard technique for measuring electrical phase
has been to read a voltage that is proportional to phase and also
to frequency. This type of circuit can be calibrated for use with a
single frequency as changing the frequency would cause the
calibration data to be incorrect.
This can also be seen with single frequency systems. The corrected
phase value will draft due to variation in the circuit
parameters.
The other typical approach is to, utilize a microprocessor to
compare the value of the phase detector output with that of a
frequency detector and compute the true phase. This approach is
fairly complex and is subject to drift of the individual circuits
as well as resolution limitations.
A block diagram 170 as shown in FIG. 10 is representative of an
improved phase detector suitable for performing the method in
accordance with the present invention. Each of the function blocks
shown comprises conventional state-of-the-art circuitry of typical
design and components for producing the function represented by
each block as hereinafter described.
The voltage input 172 and current 174 from a phacoemulsification
handpiece 40 is converted to an appropriate signal using an
attenuator 176 on the voltage signal to the phacoemulsification
handpiece, and a current sense resistor 178 and fixed gain
amplifier for the handpiece 40 current.
Thereafter, an AC voltage signal 180 and AC current signal 182 is
passed to comparators 184, 186 which convert the analog
representations of the phacoemulsification voltage and current to
logic level clock signals.
The output from the comparator 184 is fed into a D flip flop
integrated circuit 190 configured as a frequency divide by 2. The
output 192 of the integrated circuit 190 is fed into an operational
amplifier configured as an integrator 194. The output 196 of the
integrator 194 is a sawtooth waveform of which the final amplitude
is inversely proportional to the handpiece frequency. A timing
generator 198 uses a clock synchronous with the voltage signal to
generate A/D converter timing, as well as timing to reset the
integrators at the end of each cycle.
This signal is fed into the voltage reference of an A/D converter
via line 196.
The voltage leading edge to current trailing edge detector 200 uses
a D flip flop integrated circuit in order to isolate the leading
edge of the handpiece voltage signal. This signal is used as the
initiation signal to start the timing process between the handpiece
40 voltage and handpiece 40 current.
The output 102 of the leading detector 200 is a pulse that is
proportional to the time difference in occurrence of the leading
edge of the handpiece 40 voltage waveform and the falling edge of
the handpiece current waveform.
Another integrator circuit 204 is used for the handpiece phase
signal 202 taken from the detector 200. The output 206 of the
integrator circuit 204 is a sawtooth waveform in which the peak
amplitude is proportional to the time difference in the onset of
leading edge of the phacoemulsification voltage and the trailing
edge of the onset of the handpiece current waveform. The output 206
of the integrator circuit 204 is fed into the analog input or an
A/D (analog to digital converter) integrated circuit 210.
Therefore, the positive reference input 196 to the A/D converter
210 is a voltage that is inversely proportional to the frequency of
operation. The phase voltage signal 196 is proportional to the
phase difference between the leading edge of the voltage onset, and
the trailing edge of the current onset, as well as inversely
proportional to the frequency of operation. In this configuration,
the two signals Frequency voltage reference 196 and phase voltage
146 track each other over the range of frequencies, so that the
output of the A/D converter 210 produces the phase independent of
the frequency of operation.
The advantage of utilizing this approach is that the system
computer 118 (see FIGS. 1 and 2) is provided with a real time
digital phase signal that 0 to 255 counts will consistently
represent 0 to 359 degrees of phase.
The significant advantage is that no form of calibration is
necessary since the measurements are consistent despite the
frequencies utilized.
For example, using AMPs operation frequencies of 38 kHz and 47 kHz
and integrator having a rise time of 150.times.10.sup.3 V/2 and an
8 bit A/D converter having 256 counts, a constant ratio is
maintained and variation in frequency does not affect the results.
This is shown in the following examples.
EXAMPLE 1
38 KHz Operation
Actual Number of A/C counts for 90 degrees at 38 KHz
EXAMPLE 2
47 KHz Operation
A plot of phase angle as a function of frequency is shown in FIG.
11 for various handpiece 40 loading, a no load (max phase), light
load, medium load and heavy load.
With reference to FIG. 12, representing max phase mode operation,
the actual phase is determined and compared to the max phase. If
the actual phase is equal to, or greater than, the max phase,
normal aspiration function is performed. If the actual phase is
less than the max phase, the aspiration rate is changed, with the
change being proportionate to the change in phase.
FIG. 13 represents operation at less than max load in which load
(see FIG. 11) detection is incorporated into the operation, a
method of the present invention.
As represented in FIG. 12, representing max phase mode operation,
if the handpiece aspiration line 140 is occluded, the phase sensed
by phase detector sensor 128 will decrease (see FIG. 11). The
computer 118 has operator-settable limits for aspiration rates,
vacuum levels and ultrasonic power levels. As illustrated in FIG.
12, when the phase sensed by phase detector 128 reaches a
predetermined level as a result of occlusion of the handpiece
aspiration line 140, computer 118 instructs pump speed controller
120 to change the speed of the peristaltic pump 114 which, in turn,
changes the aspiration rate.
It will be appreciated that, depending upon the characteristics of
the material occluding handpiece 40, the speed of the peristaltic
pump 114 can either be increased or decreased. When the occluding
material is broken up, the phase detector 128 registers an increase
in phase angle, causing computer 118 to change the speed of
peristaltic pump 114 to an unoccluded operating speed.
In addition to changing the phacoemulsification parameter of
aspiration rate by varying the speed of the peristaltic pump 114,
the power level and/or duty cycle of the ultrasonic power source 16
can be varied as a function of the occluded or unoccluded condition
of handpiece 40.
Although there has been hereinabove described a method and
apparatus for controlling a phacoemulsification handpiece utilizing
the voltage current phase relationship of the piezoelectric
phacoemulsification handpiece in accordance with the present
invention, for the purpose of illustrating the manner in which the
invention may be used to advantage, it should be appreciated that
the invention is not limited thereto. Accordingly, any and all
modifications, variations, or equivalent arrangements which may
occur to those skilled in the art, should be considered to be
within the scope of the present invention as defined in the
appended claims.
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